DESCRIPTION (Applicant's Abstract): We propose to continue the most complete, prospective, longitudinal study of growth and development yet undertaken of children at high risk of obesity. The study of 78 children, now 32 to 53 months of age, selected on the basis of maternal obesity or leanness, has already achieved its initial goal: it has disconfirmed, the results of an influential study and the associated, widely held belief that a low total energy expenditure (TEE) and maternal obesity predict body size and composition at 1 year of age. Instead, it has found, unexpectedly, that the two independent measures of energy intake at 3 months of age predict body size and composition at 1 year of age. We now propose to search further for the risk factors for obesity in this large, carefully studied cohort as it enters the early childhood years. After 24 months in which there was minimal evidence of genetic influence, our high risk strategy has begun to bear fruit: at 30 months 14% of our sample now exceeds the 95th percentile of weight for height. As at 3 and 24 months, and now at 48 months, we will assess, at 6 and at 8 years, the influence of maternal and paternal body mass index (BMI = kg/m2), subject's body weight, TEE and resting metabolic rate. In addition, to identify behaviors that might be modified in programs of obesity prevention, we will continue to measure food intake (both 3-day records and test meals), taste (especially fat) preferences and psychosocial factors that have been implicated in the development of obesity. These efforts will be greatly enhanced by the ability (for the first time) to assess the environmental factors in a cohort that has been defined genetically as being at high risk for obesity and where metabolic status is known. Our ultimate objective is to identify behaviors that contribute to adiposity and that might be modified in programs of prevention and treatment.